I disagree with Plato90s (which is probably obvious already). Plato90s made some unsupported assumptions:
1. Traveling on a one-way ticket. This is not reported by the New York Times.
2. Secret Service agents on presidential detail do not normally travel commercial. As one who worked for a time in the White House complex during the Reagan years, I can say with certainty that this is not true. Many Secret Service agents travel in advance of the President, for lots of obvious reasons, and they indeed travel commercial. Nothing unusual about it.
If this country is going to continue being America as we have known it, then idiotic nonsense like this has got to end immediately. Air crews cannot merely say, "I'm uncomfortable with this guy on 'my' plane," and get away with having the guy thrown off. The guy has rights, too, even if he is a Secret Service agent (joke!).
My opinion: If the flight crew is uncomfortable in situations this innocuous, then THEY should get off -- perhaps permanently.
I am now putting on my asbestos suit.
Bruce